1. Field of the Invention
The present invention generally relates to printheads for inkjet printers.
2. State of the Art
FIG. 1 shows an example of a conventional printhead for a thermal inkjet printer. The printhead includes a substrate 1, an intermediate layer 2, and an orifice plate 3. A nozzle 4 is formed in the orifice plate, and a vaporization cavity 5 is defined between the substrate and the orifice plate. For convenience of illustration, the drawing shows only one of the nozzles in the orifice plate; however, a complete inkjet printhead includes an array of circular nozzles, each of which is paired with a vaporization cavity. Moreover, a complete inkjet printhead includes channels that connect vaporization cavities to an ink supply.
Furthermore, in a complete printhead, each vaporization cavity includes a heater resistor such as the resistor 6 in FIG. 1. In practice, the heater resistors on a printhead are connected in an electrical network for selective activation. When a particular heater resistor receives a pulse, the electrical energy is rapidly converted to heat which then causes ink adjacent to the heater resistor to form a vapor bubble 7. As the vapor bubble expands due to the heat provided by an energized heater resistor, the bubble ejects a droplet of ink from the nozzle in the orifice plate. This action is schematically illustrated in FIG. 1 with the direction of bubble growth being indicated by the arrow. By appropriate selection of the sequence of energizing the heater resistors, the ejected ink droplets can form patterns such as alphanumeric characters.
In practice, the quality of print provided by inkjet printers depends upon the physical characteristics and relative positioning of the ink ejection nozzles, resistors, vaporization cavities and ink inlet channels. More particularly, the design of these elements in a printhead determine the size, trajectory, frequency response and speed of ink drop ejection. In some instances, geometry can affect the ejection of ink from adjacent nozzles crosstalk.
There are several shortcomings to conventional processes for fabricating inkjet printheads. One shortcoming is that an accurate positioning step is required as the nozzle plate is assembled together with the substrate. This positioning step is costly because of the time and expensive equipment required. A further shortcoming of conventional processes occurs during the temperature cycling which a printhead experiences during use. This cycling sets up stresses and strains in the assembly since the nozzle plate and substrate have differing coefficients of thermal expansion. These stresses and strains can cause delamination of the part under extreme cases.